Potted electric coil and hair-like lead wire assembly



April 12, 1966 T.'A. WILEY 3, 7

POTTED ELECTRIC COIL AND HAIR-LIKE LEAD WIRE ASSEMBLY Filed Feb. 18, 1964 Fig. 2

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Thomas A. Wiley 27 34 33 28 BY Fly. 4

A Horn 6] United States Patent 3,246,272 POTTED ELEfiTRlC COEL AND HAIR-LIKE LEAD WIRE ASSEMBLY Thomas A. Wiley, Qverland Parlr, Kans, assignor to the United States of America as represented by the United States Atomic Energy Commission Filed Feb. 18, 1964, Ser. No. 345,815 Claims. (Cl. 336-192) The present invention relates generally to assemblies employing electrical coils and more particularly to mounting means for coupling lead wires of such coils to external circuits.

The manufacture of electronic assemblies embodying coils made up of many turns of very fine wire is accomplished at considerable expense and difficulty; nevertheless, when these assemblies are secured to external con ducting elements, they sometimes operate improperly or even fail to operate because of the relatively intricate but inadequate methods or procedures heretofore used in fastening the line wires of the coils to the conducting elements.

The very fine or hair-like wires used in coils of some transformers, magnetic amplifiers, or the like normally range in size from about four-thousandths to onethousandth of an inch in diameter or 38 to 50 American wire gage (AWG). Wire in or near this size range is so highly fragile that direct attachment to conducting elements on printed circuit boards or other items would almost invariably cause a malfunction of a circuit or system because of wire breakage. Thus, in order to avoid these shortcomings, the ends of the fine wires in or near the noted size range are generally first connected to wires of much larger diameters by wrapping the very fine coil wires several times about the larger wires and then soldering them in place. Each connection and a length of the larger wire adjacent the connection is then oriented on or in the coil body as to be folded-back upon itself and secured in this position by wrapping tape over the wires to hold them against the coil body. With this arrangement it has been hoped that the very thin coil wires are substantially relieved of external mounting strains since the folds or reverse bends in the large Wires are held by the tapein such a manner that the strains are, hopefully, taken up by the tape and the larger wires.

Unfortunately the use of the larger wires for mounting or attaching coils and the like to the external circuits, e.g., printed circuit boards, has several drawbacks or shortcomings which reflect heavily upon their acceptance in industry. One such drawback or shortcoming is the increased cost of manufacturing due to the time consuming and difiicult procedure of attaching these larger wires to the coil lead wires as aforementioned. Another is the failure of the mechanical joint between the larger and smaller wires that could and often does result from handling prior to use of the part. In order to inspect this joint before usage the electrical device must be partially disassembled by removingthe tape covering the joint, which removal may cause the joint to be sufiiciently weakened as to subsequently fail. Furthermore, in some instances a proper joint inspection cannot be readily made sinceif the electrical device has a plurality of windings, some of the joints will most likely be embedded under several layers of wires, thus rendering the inspection impractical because of the disassembling required. The number of larger wires extending from the windings, particularly from the devices having multiple windings, also presents a troublesome problem since confusion in connecting these wires to external circuits may easily result. Color coding these wires has been employed in attempting to alleviate this confusion; but even with color coding, the wires are sometimes improperly connected to the external circuits.

3,246,272 Patented Apr. 12, 1966 The aforementioned and other shortcomings of previous devices have been minimized or substantially completely eliminated by the new and improved mounting assembly for transformers, magnetic amplifiers, or the like as constructed in accordance with the present inventron.

An object of the present invention is to provide a mounting assembly wherein very thin lead wires extending from an electrical coil, or a plurality of such coils, or the like are fixedly attached to conducting elements to form a secure, relatively non breakable connection therebetween and with the conducting elements oriented in a preselected pattern.

Another object of the present invention is to affix the fine lead wires extending from a coil or a plurality of such coils to a mounting platform and thereafter enclosing the coil or coils and platform in a synthetic resin body.

Another object of the present invention is to couple fine lead wires extending from at least one coil or the like to connector pins arranged in a particular orientation for facilitating subsequent attachment to external circuitry.

A further object of the present invention is to thermally and mechanically isolate solder connections to self-leads of electrical coils for enabling the use of larger, hotter soldering irons to electrically couple the coils to external circuitry and the application of twisting moments or shock loads without affecting the self-leads or their connections.

Other and further objects of the invention will be obvious upon an understanding of the illustrative embodiments about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

Preferred embodiments of the invention have been chosen for purposes of illustration and description. The preferred embodiments illustrated are not intended to be exhaustive nor to limit the invention to the precise forms disclosed. They are chosen and described in order to best explain the principles of the invention and their application in practical use to thereby enable others skilled in the art to best utilize the invention in various embodiments and modifications as are best adapted to the particular use contemplated.

In the accompanying drawing:

FIG. 1 shows an example of a coil arrangement heretofore employed with mounting wires afiixed thereto:

FIG. 2 is a fragmentary view of the coil arrangement of FIG. 1 with sections removed for showing the connection between coil lead wires and the larger mounting wires;

FIG. 3 is a top plan view partly cut away showing various portions of one form of the present invention;

FIG. 4 is a sectional view taken generally along line 4-4 of FIG. 3 illustrating relationships of various mount components to each other and to an external circuit;

FIG. 5 is a bottom plan view of one form of the present invention showing stand-off elements used for spacing the coil mount from an external circuit panel; and

FIG. 6 is an elevational view showing another form of the present invention in which coils are mounted in a stacked relationship upon a supporting base member.

Referring to FIGS. 1 and 2 there is shown a device employing a coil such as, for example, a transformer or the like which may be of any desired configuration, but is shown in the form of a toroid for convenience of description. This device which is hereinafter referred to as the transformer 10 may comprise a multiple number of fine wire turns disposed about a suitable annular core of soft metal, powdered metal, etc., for forming the primary and secondary windings of the transformer.

The line wires used in these windings are very thin or hair-like and normally range in size from about fourthousandths to one-thousandth of an inch in diameter or 38 to 50 AWG. Inasmuch as wires of about this size range are highly fragile it is not desirable that they be utilized to support the weight of or to position the transformer, particularly in an environment subject to shocks and vibrations.

Thus, in order to provide a mounting arrangement and an electrical path from the transformer to a point of use as briefly mentioned above, the fine wires forming the transformer-windings, such as indicated at 11 in FIG. 2, are first bound against the core or on an inner winding by a suitable tape 13 of a glass-fiber composition or the like which is tightly wrapped in a spiral, overlapping fashion about the wire turns. A layer of this tape 13 is usually disposed between each winding and about the outer surface for protecting and supporting the who turns forming the coils or windings and for electrically isolating the various coils from one another, The tape 131v overlies the wire turns except for the end or self-leads of each winding; one such self-lead being shown at 15. Each of these self-leads 15 is then twisted or wrapped about an exposed end of a wire 17, which has a much larger diameter than the fine wires 11, and thereafter soldered in place. After making the connection between the self-leads 15 and the wires 17 or at any other desired time, a further layer of tape 14, which is preferably of greater strength than the tape 13, is Wrapped about the periphery or circumference of the transformer toroid and covers the wire 11 underlying the tape 13 and the selflead connection with the mounting wires 17. The wire 17 is then bent or folded back upon itself as shown in FIG. 2 and another tape 18 placed over the folded wire 17 and about the periphery of the transformer.

While only one self-lead 15 and its connection to a largerwire 17 is shown and described, many similar connections are normally used with a single transformer; for example, FIG. 1 shows six wires 17 extending from the transformer 10. A portion of these other connections are normally disposed intermediate the outer windings and the core, thus often requiring that upon the completion of a winding the connection of the self-leads to the larger wires be made prior to wrapping more turns about the underlying windings.

The technique of preparing transformers or the like for subsequent attachment to an external circuit as above described is quite complex, expensive and time consuming and still does not provide a desirable connecting link between the transformer and an external circuit for many reasons, some of which are noted above and others as will appear obvious to one examining such an arrangement.

The form of the present invention as shown in FIGS. 3 through embodies an electrical component which for convenience of description is referred to as a toroidal transformer, but may comprise other electrical devices or assemblies embodying coils, such as magnetic amplifiers and the like. This transformer 20 may comprise a multiple coil arrangement assembled in a manner somewhat similar to the above described transformer except, of course, for the use of the larger mounting wires, or by any other manufacturing technique. The coils of the transformer each comprise a desired number of turns of very fine or hair-like wire, 21 ranging in size from about four-thousandths to amout one-thousandth of an inch in diameter. Ends of these windings normally project from the coil and form leads or self-leads 22 for conveying an electrical charge to or from the transformer. In successively wrapping the various windings about the core, the free winding ends or self-leads 22 are arranged so. that they project from the transformer 21 a distance sufiicient to facilitate the attaching of these lead wires to conductive strip elements as will be described below.

In order to provide a surface to which the fragile selfleads 22 may be attached, a conductor carrying platform l 24 commonly referred to as a printed circuit board which may comprise a suitable dielectric or insulating material such as glass impregnated with a suitable synthetic resin and carrying a number of conductive strips 25 of copper or the like, has been found satisfactory. The printed circuit board or insulating base member 24 may have the conductive strips 25 placed or formed thereon in any acceptable manner such as commonly practiced by industry. These conductive strips 25 as best shown in FIG. 3 are normally equal in number to the self-leads 22 extending from the transformer 20, i.e., each of the self-leads 22 extending from the transformer 20 may be provided with its own conductive strips 25. The conductive strips 25 are preferably spaced-a slight distance apart from each other so that the attaching of the self-leads to one end of the strips 25 such as by soldering does not affect adjacent connections because of the heat generated by the soldering operation and also for providing suificient working space between adjacent connecting points. In the event the transformer has more self-leads than can be suitably accommodated by conducting strips 25 placed on one side or surface of the base member 24', it maybe desirable to place a number of these conducting strips on the other side or surface of the base member 24 remote to the transformer 20, such as shown in FIG; 3.

The insulating base member '24 may be of any desired size or configuration, but preferably corresponds generally to the peripheral dimensions of the transformer or other item being attached thereto. For example, the base member 24 shown in the drawings is of a discoid configuration having a circumference generally similar to that of the toroidal transformer 20. The conducting strips 25 are preferably oriented on the base member 24 such that the end of each strip 25 that is to be attached to the lead wires 22 is disposed adjacent a peripheral edge of the base member 24 such as to place the point of joining or soldering the lead. wires to the strips in a readily accessible location. The other ends of'each strip 25 are preferably spaced a sufficient distance from the end aflixed to a lead wire to prevent adverse heating of the soldered lead wire connection. during coupling of the transformer to external circuitry. These other ends may terminate adjacent marginal edges of the base member, or, if desired, they may terminate at any desired location on the surface of the base member 24. The conducting strips 25 are also preferably arranged .in a prescribed pattern on the base member 24 so that ends of the strips opposite the point of attachment .to the self-leads 22 may be oriented in a particular arrangement for facilitating the coupling to an external circuit as will be'hereinafter described in more detail.

The coupling of the transformer 20 to anexternal circuit, such as, for example, a printed circuit board as shown at 27 in FIGS. 3 and 4 or any other desired type mounting panel or circuitry, may be more easily accommodated by utilizing laterally extending conducting means or contact pins on the strips 25. Satisfactory results have been attained by using contact or connector pins 28 which extend from the strip elements 25 to a location below the circuit board or base member 24. These connector pins 28 may be of any desired configuration; for example, the pins may have a shank portion 29 with a beveled leading end and an annular head potrion 30 at the other end and separated from the shank portion by a thickened washer-like central portion 3-1. To attach the connector pins 28 to the strip elements '25, holes 3 2 of suflicient dimensions to receive the head portion 30 but not the central portion 31 may be drilled, punched or otherwise provided through the board 24 adjacent the ends of the strips 25 that are opposite the strip ends connected to. the self-leads 22. The pins may each be affixed to the board 24 by swaging over the uppermost end of the head portion and there-after applying a solder connection between the pin 28 and the strip element 25 to assure continuity from the self-lead to the shank end or portion 29 of the :3 pin 28. This shank portion 29 of each pin may be of any desired length, but it may be preferable to make it sufficiently long so as to substantially penetrate the thickness of the external mounting circuit, e.g., the printed circuit board 27, and thereby provide a more readily solderable arrangement.

It may also be desirable to assure a positive connection between the self-leads 22 and the strips 25 by providing the end of the strips 25 and adjacent portions of the printed circuit board 24 with throughgoing holes 33 which may be tormed in a manner similar to the holes 32. Thus, the self-leads 22 may be inserted into or passed through their respective holes 33 and thereafter soldered in place. This arrangement also facilitates the soldering of the lead wires from the underside of the base member. Of course, when the strip elements 25 are disposed on the underside of the base member 24, the holes 33 are normally preferred to establish a desirable coupling between the strip elements and the self-leads 22. Eyelets 34 of a suitable conducting material, e.g., copper and the like, may be placed in the holes 33 to facilitate the soldering.

The connector pins 28 and the self-leads 22 are preferably secured to particular ends of the strip elements 25 so as to provide a desirable arrangement or orientation of pins 28 projecting from the base member 24. For example, one such pin orientation is shown in the six pin configuration of FIG. where the pins '28 are so arranged that four of the pins are disposed adjacent the margin or edge ofthe board 24 generally opposite the marginal portion of the board carrying the other two pins 28. Pin arrangements, such as the one above described, enable the connection to be made to a panel or external circuit board with minimal errors and confusion, and overcome the previous color-coding confusion and difliculties.

When the transformer is attached to the printed circuit board or base member 24 as above described, the transformer may be moved closer to the base member 24 such as by slightly rotating it with respect to the base member 24 so as to prevent undesirable bending or positioning of the self-leads 22. if, however, the self-leads are soldered to the strips from the underside of the base member 24, such relative rotation may not be necessary since the transformer may be placed fairly close to the base member during the soldering of the self-leads. In either event it is preferable to place a suitable insulating means between the Wire turns on the transformer 20 and the strips 25 to isolate the voltages in the turns from the strips 25. This insulating means may be of any desirable material and configuraton; for example, the insulating means may comprise a thin washer-like member such as indicated in FIG. 3 at 35, or a layer of insulating tape placed across the bottom of the transformer 20. The member 35 which may be of any suitable insulating material such as paper or the like, may be secured by a suitable adhesive to the base member '24 and the transformer 20 so as to maintain the latter in a desirable orientation with respect to the base member 24 to facilitate the soldering of the self-leads 22 to the strip elements 25.

After the lead wires extending from the transformer are suitably attache-cl to the strip elements on the base member, the pins 28 being attached to opposite ends of the respective strip elements, the resulting assembly may be placed in a mold not shown) and covered with a suitable potting material such as synthetic resin or the like. The potting material 36 preferably covers or encloses the entire above described assembly except for the shank portions 29 of the connector pins 28 which are left free of the potting material so as to be subsequentially coupled to a mounting panel or an external printed circuit board.

It may be desirable to provide the potted assembly with spacing means on the underside thereof adjacent the pins 28 for providing a slight separation between the assembly and the printed circuit board 27 to assure that a suitable solder connection is attained between the connector pins 28 and the external printed circuit board.

For example, with the spacing means it is unlikely that capillary attraction could draw a portion of the liquefied solder being used to connect the assembly to the board 27 across the interface therebetween and thereby im properly couple adjacent pins 28 or otherwise affect the operation of the assembly. While several arrangements for providing this spacing or separation are available, satisfactory results have been attained by placing standoff strips 37 and 38 (FIGS. 4 and 5) substantially across the bottom of the assembly. These stand-off strips 37 and 38 may be formed from the potting material during the above mentioned potting step and be disposed in any desired orientation. However, it may be desirable to place these stand-off strips on the bottom of the assembly at such locations as to minimize tilting of the assembly.

It may be preferred to use a translucent or clear resin as the potting material so as to provide for readily inspecting the lead wires 22 and their connections to the strips 25. Also, it may be desirable to provide the base member 24 with an aperture 39 adjacent the center thereof to facilitate the potting of the transformer assembly by enabling the potting material to more readily flow into available spaces adjacent the platform and in preventing the formation of air pockets. A similar aperture may be provided in the washer-like insulating member 35.

While the above description of the present invention is directed to a toroidal transformer with six leads (FIG. 5) disposed on a discoid base member, it is to be understood that the present invention is not limited to such and may be any desired electrical component such as a magnetic amplifier, a magnetic memory core, and the like, using any number of fine lead wires, and affixed to a base member of any desirable configuration. For example, a toroidal magnetic amplifier Withsay, four selfleads may be mounted on its edge and afiixed to a dielectric Zbase member of a generally rectangular configuration.

Referring now to FIG. 6, there is shown another form of the present invention in which a plurality of the above noted electrical devices may be placed in a stacked relationship on a common base member. The various components shown in this figure may be essentially similar to the components shown in FIGS. 35. Consequentially, reference characters similar to those used in FIGS. 3-5, except for the addition of a sufiix a will be used to indicate corresponding structures in the FIG. 6 assembly.

In FIG. 6 a pair of mounted electrical devices are shown and may have similar or dissimilar electrical characteristics, but for convenience of description are hereinafter referred to as a pair of coils or toroids Zita. These toroids Ztla are preferably of different circumferential dimensions and so placed upon the base member 24a that the toroid having the lesser dimension is nearest the base member 24a. In other words, the toroids 20a are disposed in what may be referred to as an inverted-cone arrangement.

The stacking of toroids in the noted fashion sets forth desirable features in that the proper securing of the selfleads 22a to the strip elements is more readily attainable since the possibility of confusing the various lead wires is substantially minimized. Also, by placing the smaller toroid closer to the base member the possibility of effecting an undesirable electrical coupling between the leadwires of an upper toroid and the windings or lead Wires of a lower or underlying toroid is substantially alleviated.

When assembling such a multiple coil device it may be preferable to electrically isolate the coils 29a from each other. This isolating may be readily attained by placing suitable insulating means such as washer-like members 35a at the interface between adjacent coils and intermediate the base member and the smaller coil. These washer-like members 3501 may be coated with a suitable adhesive to join or bond the coil elements to the base member and thereby aid in the attaching. of the lead wires to the strip elements and in maintaining the stacked relationship of the coils prior to the potting operation. The coils may be placed in position one at the time so that the lead wires 22a. extending from each coil may be joined to the strip elements prior to the joining of the lead wires from another coil. However, if desired the coils may be stacked prior to joining the lead wires to the strip elements.

While only a pair of coils 20a are described it will appear clear that any desired number and configuration of coils and other electrical devices may be stacked on a common base member.

It will be seen that the present invention sets forth a unique and highly improved unit or mounting assembly which may be stored for an indefinite duration without degradation. Inasmuch as the entire assembly except for the ends of the contact pins is encapsulated or potted, minimal care is required during handling. The strip elements lengths on the base member provide thermal isolation in that during the soldering of the contact pins to an external panel the solder connection of the self-leads is thermally shielded, which feature facilitates the use of a larger and hotter soldering iron to connect the contact pins to the panel. Mechanical isolation is also provided by the strip elements since twisting moments or shock and vibration loads placed upon the contact pins or the potted assembly can not affect the self-lead connection. Another feature of the present invention is in the use of the printed circuit board or base member which facilitates the standardizing of the connections, speeds assembly operations, and provides a suitable mounting for the contact pins.

As various changes may be made in the form, construction and arrangement of the parts herein without departing from the spirit and scope of the invention and without sacrificing any of its advantages, it is to be understood that all matter herein is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. An electrical coil assembly comprising a coil of hairlike wire having a plurality of spaced apart hair-like wires thereof of diameter from about four thousandths to about one thousandth of an inch protruding from the coil, a dielectric base member carrying a plurality of elongated conductor strip elements integral therewith, each strip element having one end thereof disposed adjacent to an outer peripheral portion of the coil and to a marginal portion of the base member and adjacent to one of said protruding wires and another end thereof spaced from said one end and disposed adjacent to an .8 outer peripheral portion of the coil and to a marginal portion of the base member, each of said protruding hair-like wires being directly secured to said one end. of each strip element, and a plurality of spaced apart exposed connector pins carried by and projecting beyond said base member in a direction away from said. coil with each pin being rigidly atfixed to said base member and connected to one of said strip elements at a location adjacent said other end thereof.

2. The device of claim 1 in. which said other end of each stri-p element is disposed adjacent a marginal portion of said base member that is located generally opposite said first mentioned marginal portion.

3. The device of claim 1 in which said exposed connector pins project beyond the dielectric base member surface facing away from said assembly and coil, and wherein an insulating apertured washer is disposed intermediate the base member and the coil and electrically isolates the latter from the strip elements.

4. The device of claim 1 in which said coil, said pro truding hair-like wires of the coil, and both surfaces of said dielectric base member are enclosed and fixedly retained by a potting material, and a pair of spaced apart ribs. of potting material extend from and provide projections at a surface of the dielectric base member facing away from said coil for non tiltably spacing the base. member and the resin potting material from a mounting panel.

5. The device of claim 1 inwhich a pair of said coils of different peripheral dimensions are disposed in superposed relationship, withlthe coil of lesser dimension dis-. posed intermediate the base member and the other of said coils, and wherein an insulating washer coated 1th adhesive material is intermediate the coils and ecures the coils to one another, and wherein an. additi nal adhesive coated insulating washer is intermediate the base, member and the nearest coil to maintain the coils in position with respect to the base member.

References Cited by the Examiner UNITED STATES PATENTS 1,633,047 6/1927 St.,]ames 336208 X 1,702,159 2/1929 Grunow 336- 492 X 2,391,038 12/1945 Rife-nbergh 336205 X: 2,731,607 1/1956 Gould et al. 33696' 2,915,723 12/ 1959 Wennerberg 336-229. 2,993,262 7/1961 Ross et al. 336-192 X LARAMIE E. ASKIN, Primary Examiner.

JOHN F. BURNS, T. J. KOZMA, Assistant Examiners. 

1. AN ELECTRICAL COIL ASSEMBLY COMPRISING A COIL OF HAIRLIKE WIRE HAVING A PLURALITY OF SPACED APART HAIR-LIKE WIRES THEREOF OF DIAMETER FROM ABOUT FOUR THOUSANDTHS TO ABOUT ONE THOUSANDTH OF AN INCH PROTRUDING FROM THE COIL, A DIELECTRIC BASE MEMBER CARRYING A PLURALITY OF ELONGATED CONDUCTOR STRIP ELEMENTS INTEGRAL THEREWITH, EACH STRIP ELEMENT HAVING ONE END THEREOF DISPOSED ADJACENT TO AN OUTER PERIPHERAL PORTION OF THE COIL AND TO A MARGINAL PORTION OF THE BASE MEMBER AND ADJACENT TO ONE OF SAID PROTRUDING WIRES AND ANOTHER END THEREOF SPACED FROM SAID ONE END AND DISPOSED ADJACENT TO AN OUTER PERIPHERAL PORTION OF THE COIL AND TO A MARGINAL PORTION OF THE BASE MEMBER, EACH OF SAID PROTRUDING HAIR-LIKE WIRES BEING DIRECTLY SECURED TO SAID ONE END OF EACH STRIP ELEMENT, AND A PLURALITY OF SPACED APART EXPOSED CONNECTOR PINS CARRIED BY AND PROJECTING BEYOND SAID BASE MEMBER IN A DIRECTION AWAY FROM SAID COIL WITH EACH PIN BEING RIGIDLY AFFIXED TO SAID BASE MEMBER AND CONNECTED TO ONE OF SAID STRIP ELEMENTS AT A LOCATION ADJACENT SAID OTHER END THEREOF. 